Motion(theory questions) Flashcards
Does a car’s odometer measure distance traveled or displacement?
Distance traveled
There is a distinction between average speed and the magnitude of average velocity. Give an
example that illustrates the difference between these two quantities
Average speed is the total distance traveled divided by the elapsed time. If you go for a walk,
leaving and returning to your home, your average speed is a positive number. Since Average
velocity = Displacement/Elapsed time, your average velocity is zero
If you divide the total distance traveled on a car trip (as determined by the odometer) by the
elapsed time of the trip, are you calculating average speed or magnitude of average velocity?
Under what circumstances are these two quantities the same?
Average speed. They are the same if the car doesn’t reverse direction
Is it possible for speed to be constant while acceleration is not zero?
No, in one dimension constant speed requires zero acceleration.
Give an example in which velocity is zero yet acceleration is not.
A ball is thrown into the air and its velocity is zero at the apex of the throw, but acceleration is
not zero.
An object that is thrown straight up falls back to Earth. This is one-dimensional motion. (a)
When is its velocity zero? (b) Does its velocity change direction? (c) Does the acceleration have
the same sign on the way up as on the way down?
a. at the top of its trajectory; b. yes, at the top of its trajectory; c. yes
State two scenarios of the kinematics of single object where three known quantities require
two kinematic equations to solve for the unknowns.
If the acceleration, time, and displacement are the knowns, and the initial and final velocities are
the unknowns, then two kinematic equations must be solved simultaneously. Also if the final
velocity, time, and displacement are the knowns then two kinematic equations must be solved for
the initial velocity and acceleration.
When given the acceleration function, what additional information is needed to find the
velocity function and position function?
We must know the initial conditions on the velocity and position at t = 0 to solve for the
constants of integration.
A car is 2.0 km west of a traffic light at t = 0 and 5.0 km east of the light at t = 6.0 min.
Assume the origin of the coordinate system is the light and the positive x direction is eastward.
(a) What are the car’s position vectors at these two times? (b) What is the car’s displacement
between 0 min and 6.0 min?
7 m east
The position of a particle moving along the x-axis is given by xt t ( ) 4.0 2.0 = − m. (a) At
what time does the particle cross the origin? (b) What is the displacement of the particle between
t 3.0 s = and t 6.0 s?
-6 m
KYK NA GRAFIEKE VRAE
A particle moves in a straight line at a constant velocity of 30 m/s. What is its displacement
between t = 0 and t = 5.0 s?
150 m
A particle moves in a straight line with an initial velocity of 30 m/s and constant acceleration
30 m/s2
. (a) What is its displacement at t = 5 s? (b) What is its velocity at this same time?
180 m/s
A bullet in a gun is accelerated from the firing chamber to the end of the barrel at an average
rate of 5 2 6.20 10 m/s × for 4 8.10 10 s. − × What is its muzzle velocity (that is, its final velocity)?
502.2 m/s
A powerful motorcycle can accelerate from rest to 26.8 m/s (100 km/h) in only 3.90 s. (a)
What is its average acceleration? (b) Assuming constant acceleration, how far does it travel in
that time?
52.26 m
A care package is dropped out of a cargo plane and lands in the forest. If we assume the care
package speed on impact is 54 m/s (123 mph), then what is its acceleration? Assume the trees
and snow stops it over a distance of 3.0 m.
-486 m/s^2
There is a 250-m-high cliff at Half Dome in Yosemite National Park in California. Suppose a
boulder breaks loose from the top of this cliff. (a) How fast will it be going when it strikes the
ground? (b) Assuming a reaction time of 0.300 s, how long a time will a tourist at the bottom
have to get out of the way after hearing the sound of the rock breaking loose (neglecting the
height of the tourist, which would become negligible anyway if hit)? The speed of sound is 335.0
m/s on this day.
6.09 s
A particle at rest leaves the origin with its velocity increasing with time according to v(t) =
3.2t m/s. At 5.0 s, the particle’s velocity starts decreasing according to [16.0 – 1.5(t – 5.0)] m/s.
This decrease continues until t = 11.0 s, after which the particle’s velocity remains constant at
7.0 m/s. (a) What is the acceleration of the particle as a function of time? (b) What is the position
of the particle at t = 2.0 s, t = 7.0 s, and t = 12.0 s?
116m
What form does the trajectory of a particle have if the distance from any point A to point B is
equal to the magnitude of the displacement from A to B?
straight line
If the instantaneous velocity is zero, what can be said about the slope of the position function?
The slope must be zero because the velocity vector is tangent to the graph of the position
function.
If an object has a constant x-component of the velocity and suddenly experiences an
acceleration in the y direction, does the x-component of its velocity change?
No, motions in perpendicular directions are independent.
Answer the following questions for projectile motion on level ground assuming negligible air
resistance, with the initial angle being neither 0° nor 90 : ° (a) Is the velocity ever zero? (b)
When is the velocity a minimum? A maximum? (c) Can the velocity ever be the same as the
initial velocity at a time other than at t = 0? (d) Can the speed ever be the same as the initial
speed at a time other than at t = 0?
a. no; b. minimum at apex of trajectory and maximum at launch and impact; c. no, velocity is a
vector; d. yes, where it lands
A dime is placed at the edge of a table so it hangs over slightly. A quarter is slid horizontally
on the table surface perpendicular to the edge and hits the dime head on. Which coin hits the
ground first?
They both hit the ground at the same time
Can tangential acceleration change the speed of a particle undergoing circular motion?
yes
A basketball player dribbling down the court usually keeps his eyes fixed on the players
around him. He is moving fast. Why doesn’t he need to keep his eyes on the ball?
If he is going to pass the ball to another player, he needs to keep his eyes on the reference frame
in which the other players on the team are located.
The coordinates of a particle in a rectangular coordinate system are (1.0, –4.0, 6.0). What is
the position vector of the particle?
r (->) = 1i - 4j + 6k
DOEN PROBLEMS https://stemlearn.sun.ac.za/pluginfile.php/143015/mod_resource/content/1/UniversityPhysicsVolume1-Ch04.pdf
bladsy 2-13
JAAAAA :(
